Clutches are used in a wide variety of applications to selectively couple power from a first rotatable "driving" member, such as a driving disk or plate, to a second, independently-rotatable "driven" member, such as a driven plate or disk. In one known variety of clutches, commonly referred to as "one-way" or "overrunning" clutches, the clutch "engages" to mechanically couple the driving member to the driven member only when the driving member seeks to rotate in a first direction relative to the driven member. Once so engaged, the clutch will release or decouple the driven member from the driving member only when the driving member rotates in a second, opposite direction relative to the driven member. Further, the clutch otherwise permits the driving member to freely rotate in the second direction relative to the driven member. Such "free-wheeling" of the driving member in the second direction relative to the driven member is also known as the "overrunning" condition.
One such known one-way clutch employs juxtaposed, nominally-coaxial driving and driven members featuring generally planar clutch faces in closely-spaced axial opposition. Such "planar" one-way clutches, as taught by Frank in U.S. Pat. No. 5,449,057 and Ruth et al. in U.S. Pat. No. 5,597,057, typically include a plurality of recesses or "pockets" formed in the face of the driving member and at least as many recesses or "notches" formed in the face of the driven member. A thin, flat pawl or strut, whose width is significantly less than its length, is carried within each of the driving member's pockets such that a first longitudinal end of each strut may readily engage and bear against a radial shoulder defined by its respective pocket in the driving member. The strut's second, opposite longitudinal end is urged towards and against the face of the driven member, for example, by a spring positioned in the pocket beneath the strut.
When the driving member rotates in the first direction relative to the driven member, the second end of at least one strut engages and thereafter bears against a radial shoulder defined by a notch in the driven member, whereupon the strut is placed in compression and the driven member is coupled for rotation with the driving member. When the driving member rotates in the second direction relative to the driven member, a ramped surface defined by other portions of the driven member's notches urge the second end of each strut back towards the driving member, whereupon the driving member is permitted to freely rotate in the second direction relative to the driven member.
In order to improve the quality of the strut-member engagement, the member-engaging ends of each strut are each provided with a canted surface, each nominally parallel with the other. And, in U.S. Pat. No. 5,597,057, Ruth et al. further teach use of a strut whose first end includes a pair of oppositely-projecting "arms" or "ears," the top surface of which is ramped to prevent interference between the top of each ear and the driven member as the second end of the strut is biased towards the driven member. By way of example, where the radial shoulders defined in each of the driving and driven members extend in a direction substantially normal to each member's generally planar clutch face, the ramped top surface of each ear is inclined roughly the same angle as each of the strut's canted end surfaces. A portion of each ear adjacent to the canted surface of the strut's first end is also preferably removed to form a relief which ensures that the strut's ears will not be loaded during clutch engagement.
While struts with parallel, canted end surfaces and ramped ears provide these prior art planar one-way clutches with increased performance, the presence of these features significantly increases the manufacturing costs associated with these thin, flat struts. For example, in accordance with one known process, the struts used in these planar one-way clutches are fine blanked in laterally-adjacent pairs from relatively-thin coil stock in a five-step process: (1) the coil stock is coined to provide the appropriate ramp angle on that which will become the strut's ears; (2) the stock is "U"-trimmed to define the outer periphery of the ears; (3) the stock is further trimmed to define the sides of the strut; (4) the edges of the web are formed down as by bending the web over a horn to thereby provide an inverted "V," each leg of which descends at the nominal angle with which the strut's member-engaging end surfaces are to be formed; and (5) the lateral pair of struts are blanked out of the descending legs of the web, one from each leg, as the punch pierces through the web on an angle. As a further disadvantage, this prior art process is performed at a relatively slow rate of perhaps about 18 to 20 strokes per minute.
The canted end surfaces of these blanked prior art struts typically feature about 10 percent breakout and substantial roll over. The resulting end surface distortions reduce the amount of available member-engaging end surface contact area on each strut, even after the costly subsequent machining of the end surfaces. Perhaps more significantly, the difficulty of controlling both the down angle of the web as it is bent over the horn and the subsequent angle at which the punch shears each of the strut's end surfaces combines with the end surface distortions to result in reduced dimensional control, including relatively poor control of the angle at which each of the strut's end surfaces is canted, and an attendant loss of parallelism between the strut's end surfaces.